Granular detergent compositions have, in the past, often contained high concentrations of phosphate builder materials, particularly sodium tripolyphosphate. When a crutcher mix containing sodium tripolyphosphate is spray-dried, it is believed that enough mixed-phosphate hydrolysis products are formed to inhibit phosphate crystal growth. The hydrolysis products are concentrated in the liquid phase which finally dries to an amorphous glassy phosphate material. This glassy material effectively "cements" the finely crystalline granule walls together, producing granules which exhibit very desirable physical properties, i.e., crisp, durable and free-flowing granules. Moreover, the glassy phosphate material readily disintegrates in the laundering solution so that no insoluble residue is left on the fabrics.
Alkali metal silicates are usually included in granular detergents at low levels for corrosion inhibition and processing reasons. When phosphate builders are removed from detergents, the level of silicate is often increased severalfold since it also dries to a tough glassy film capable of strengthening granule walls and enhancing free-flowing characteristics. Silicates having a lower SiO.sub.2 to alkali metal oxide ratio (e.g., 1.6-2.0) are usually selected because they are more water-soluble than the higher ratio silicates. However, exposure of the silicate to carbon dioxide during drying and storage can shift its ratio to a higher value and reduce its solubility, resulting in detergent granules which do not completely disintegrate in the laundering solution, and an unacceptably high level of insoluble material being deposited on fabrics. The insolubles problem can be particularly severe when the detergent composition also contains water-insoluble aluminosilicate material since higher levels of silicates (e.g., above about 3%) enhance the deposition of the aluminosilicates onto fabrics. This solubility problem is compounded further in a pouched detergent form product.
An annoying problem with air/water-permeable pouched granular detergent is dusting when the pouch is removed from its package for use in the washing machine.
The use of hygroscopic builders, particulatly at higher levels, can improve granular detergent solubility. However, they have been avoided in granular form due to granular stickiness and caking upon storage. Detergent stickiness and caking are usually associated with decreased solubility and undesirable flow properties.